ptp: add debugfs interfaces to loop back the periodic output signal

For some PTP devices, they have the capability to loop back the periodic
output signal for debugging, such as the ptp_qoriq device. So add the
generic interfaces to set the periodic output signal loopback, rather
than each vendor having a different implementation.

Show how many channels support the periodic output signal loopback:
$ cat /sys/kernel/debug/ptp<N>/n_perout_loopback

Enable the loopback of the periodic output signal of channel X:
$ echo <X> 1 > /sys/kernel/debug/ptp<N>/perout_loopback

Disable the loopback of the periodic output signal of channel X:
$ echo <X> 0 > /sys/kernel/debug/ptp<N>/perout_loopback

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20250905030711.1509648-2-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/ptp/ptp_clock.c

@@ -248,6 +248,69 @@ static void ptp_aux_kworker(struct kthread_work *work)
 		kthread_queue_delayed_work(ptp->kworker, &ptp->aux_work, delay);
 }
 
+static ssize_t ptp_n_perout_loopback_read(struct file *filep,
+					  char __user *buffer,
+					  size_t count, loff_t *pos)
+{
+	struct ptp_clock *ptp = filep->private_data;
+	char buf[12] = {};
+
+	snprintf(buf, sizeof(buf), "%d\n", ptp->info->n_per_lp);
+
+	return simple_read_from_buffer(buffer, count, pos, buf, strlen(buf));
+}
+
+static const struct file_operations ptp_n_perout_loopback_fops = {
+	.owner	= THIS_MODULE,
+	.open	= simple_open,
+	.read	= ptp_n_perout_loopback_read,
+};
+
+static ssize_t ptp_perout_loopback_write(struct file *filep,
+					 const char __user *buffer,
+					 size_t count, loff_t *ppos)
+{
+	struct ptp_clock *ptp = filep->private_data;
+	struct ptp_clock_info *ops = ptp->info;
+	unsigned int index, enable;
+	int len, cnt, err;
+	char buf[32] = {};
+
+	if (*ppos || !count)
+		return -EINVAL;
+
+	if (count >= sizeof(buf))
+		return -ENOSPC;
+
+	len = simple_write_to_buffer(buf, sizeof(buf) - 1,
+				     ppos, buffer, count);
+	if (len < 0)
+		return len;
+
+	buf[len] = '\0';
+	cnt = sscanf(buf, "%u %u", &index, &enable);
+	if (cnt != 2)
+		return -EINVAL;
+
+	if (index >= ops->n_per_lp)
+		return -EINVAL;
+
+	if (enable != 0 && enable != 1)
+		return -EINVAL;
+
+	err = ops->perout_loopback(ops, index, enable);
+	if (err)
+		return err;
+
+	return count;
+}
+
+static const struct file_operations ptp_perout_loopback_ops = {
+	.owner   = THIS_MODULE,
+	.open    = simple_open,
+	.write	 = ptp_perout_loopback_write,
+};
+
 /* public interface */
 
 struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
@@ -389,6 +452,12 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 	/* Debugfs initialization */
 	snprintf(debugfsname, sizeof(debugfsname), "ptp%d", ptp->index);
 	ptp->debugfs_root = debugfs_create_dir(debugfsname, NULL);
+	if (info->n_per_lp > 0 && info->perout_loopback) {
+		debugfs_create_file("n_perout_loopback", 0400, ptp->debugfs_root,
+				    ptp, &ptp_n_perout_loopback_fops);
+		debugfs_create_file("perout_loopback", 0200, ptp->debugfs_root,
+				    ptp, &ptp_perout_loopback_ops);
+	}
 
 	return ptp;
 

include/linux/ptp_clock_kernel.h

@@ -67,6 +67,8 @@ struct ptp_system_timestamp {
  * @n_ext_ts:  The number of external time stamp channels.
  * @n_per_out: The number of programmable periodic signals.
  * @n_pins:    The number of programmable pins.
+ * @n_per_lp:  The number of channels that support loopback the periodic
+ *             output signal.
  * @pps:       Indicates whether the clock supports a PPS callback.
  *
  * @supported_perout_flags:  The set of flags the driver supports for the
@@ -175,6 +177,11 @@ struct ptp_system_timestamp {
  *                scheduling time (>=0) or negative value in case further
  *                scheduling is not required.
  *
+ * @perout_loopback: Request driver to enable or disable the periodic output
+ *                   signal loopback.
+ *                   parameter index: index of the periodic output signal channel.
+ *                   parameter on: caller passes one to enable or zero to disable.
+ *
  * Drivers should embed their ptp_clock_info within a private
  * structure, obtaining a reference to it using container_of().
  *
@@ -189,6 +196,7 @@ struct ptp_clock_info {
 	int n_ext_ts;
 	int n_per_out;
 	int n_pins;
+	int n_per_lp;
 	int pps;
 	unsigned int supported_perout_flags;
 	unsigned int supported_extts_flags;
@@ -213,6 +221,8 @@ struct ptp_clock_info {
 	int (*verify)(struct ptp_clock_info *ptp, unsigned int pin,
 		      enum ptp_pin_function func, unsigned int chan);
 	long (*do_aux_work)(struct ptp_clock_info *ptp);
+	int (*perout_loopback)(struct ptp_clock_info *ptp, unsigned int index,
+			       int on);
 };
 
 struct ptp_clock;